In recent years, medical imaging has become a highly valuable tool for medical professionals. One common imaging technique is computed tomography (CT). The CT images, typically of one or more axial volumetric scans, are either analyzed individually by a radiologist or alternatively, they can be reconstructed into a three-dimensional (3D) model. Three-dimensional modeling has been used in a variety of clinical applications including virtual colonoscopies, virtual bronchoscopies, and virtual angioscopies. Using a computer-generated model from CT scans, a radiologist can pre-screen patients for cancer or other diseases. Using such a virtual model avoids subjecting the patient to a traditional manual endoscopy, which can be uncomfortable, expensive, and inaccurate.
There are several methods used to construct a volumetric representation of an object, such as when given a set of two-dimensional scans. The most common method is segmentation. Segmentation uses the image intensity of portions of a scan to determine what portions are “inside” the object to be defined, and what portions are “outside.” The output of such a segmentation process is a volumetric virtual object, which is typically represented by a collection of voxels (3D pixels) arranged in 3D space.
In a typical scan, organs, bone, and other materials appear with varying intensities along with the region of interest. For example, in a colonic scan, the lower portions of the lungs, the stomach, and the small bowel typically appear. To reduce the processing complexity, it is desirable to isolate the region of interest (e.g., the colon) and remove the excess portions (e.g., extracolonic components) from the scan.
Some of the same heuristics used in the segmentation to determine the interior and exterior of a virtual object can be reused to determine relevant and irrelevant regions in a scan. Image intensity and other characteristics such as position and size can be used to help determine relevant regions.
However, determining all of the relevant regions is made more difficult in many cases where the colon is represented as several disconnected fragments. In one instance, this can occur when there is insufficient distention of the colon, which is caused typically by suboptimal inflation. Other causes include large polyps or lesions, which can disconnect adjoining segments of the colon.